Flat panel displays are widely used in a variety of applications, including computer displays. One suitable flat panel display is a field emission display. Field emission displays typically include a generally planar emitter panel beneath a display screen. The emitter panel is a substrate having an array of surface discontinuities projecting from an upper surface. Conventionally, the surface discontinuities are conical projections, or "emitters" integral to the substrate. Contiguous groups of emitters are then grouped into emitter sets where the bases of the emitters in the emitter sets are commonly connected.
Typically, the emitter sets are arranged in an array of rows and columns, and a conductive extraction grid is positioned above the emitters. All, or a portion, of the extraction grid is driven with a voltage of about 30-120 V. The emitter sets are then selectively activated by applying a voltage to the emitter sets. The voltage difference between the emitter sets and the extraction grid produces an electric field extending from the extraction grid to the emitters. In response to the electric field, the emitter sets emit electrons.
The display screen is mounted directly above the extraction grid and is coated with a transparent conductive material to form an anode biased to about 1-2 kV. The anode attracts the emitted electrons, causing the electrons to pass through the extraction grid. A cathodoluminescent layer covers the anode and faces the extraction grid to intercept the electrons as they travel toward the 1-2 kV potential of the anode. The electrons strike the cathodoluminescent layer, causing the cathodoluminescent layer to emit light at the impact site. The emitted light then passes through the anode and display screen where it is visible to a viewer. The light emitted from each of the areas thus becomes all or part of a picture element or "pixel."
The brightness of the light produced in response to the emitted electrons depends, in part, upon the rate at which electrons strike the cathodoluminescent layer, which in turn depends upon the available current providing electrons to the emitter sets. The light intensity of each pixel is controlled by controlling the current available to the corresponding emitter set. To allow individual control of each of the pixels, each emitter set is selectively controlled by a row signal and column signal through corresponding drive circuitry. To create an image, the control circuitry separately establishes current to each of the emitter sets. Because a typical display includes several thousand pixels, the control circuitry must be able to separately address each of the emitter sets. Consequently, such field emission displays typically require relatively complex control circuitry and tightly controlled signal timing.
A further drawback of conventional field emission displays is that electrons are emitted from the points of the conical emitters which have very small cross-sectional areas. If electrons are extracted too quickly from the emitters, the resulting high current density within the emitters could damage the emitters. Thus, the rate at which electrons can be emitted must be limited, thereby limiting brightness of the pixels.
To try to overcome the problem of low current capability and to increase reproducibility, Kanemaru et al. demonstrated a segmented vertical-wedge emitter panel in Kanemaru, Ochiai, and Itoh, "Fabrication of a New Vertical Wedge Silicon Field Emitter Array," Revue: Le Vide, les Couches Minces, Suppl. No. 271, March-April 1994 (International Vacuum Manufacturing Conference 1994), which is incorporated herein by reference. Kanemaru et al. proposed an array of short, wedge-shaped emitters arranged in rows and columns. The wedge-shaped emitters act as substitutes for conical emitters and would presumably require similarly complex control circuitry.